Fid Flu & Flux

Fid= faith or trust
Bona fide (adjective): Genuine, real, true
Fidelity (noun): Faithfulness to a person, cause, or belief demonstrated by continuing loyalty and support
Infidel (noun): A person who does not believe in religion or who adheres to a religion other than ones own

Flu&Flux= flowing
Fluent (adjective): Flowing easily; a person able to express oneself easily and articulately
Confluence (noun): the junction of two rivers, rivers of approximately equal width
Influx (noun): An arrival or entry of large numbers of people or things